Well bore perforating apparatus



Oct. 10, 1967 w. T. BELL WELL BORE PERFORATING APPARATUS Filed Oct. 10, 1966 3 Sheets-Sheet 1 Q W//// 0/77 7: Be

I NVENTOR.

Oct. 10, 1967 W. T. BELL WELL BORE PERFORATING APPARATUS 5 Sheets-Sheet 2 Filed Oct. 10, 1966 IN VENTOR.

W////a/77 7. JSe/l BY ,qrr'a /fr Oct. 10, 1967 w. r. BELL WELL BORE PERFORATING APPARATUS 3 Sheets-Sheet 3 Filed Oct. 10, 1966 1N VEN TOR ATTO NE) United States Patent 3,346,057 WELL llORE PERFGRATING APPARATUS William T. Bell, Houston, Tex., assignor to Schlurnberger Technology Corporation, Houston, Tex, a corporation of Texas Filed Oct. 10, 1966, Ser. No. 601,248 21 Claims. (Cl. 175-452) This application is a continuation-in-part of my pending application, Ser. No. 409,374, filed Nov. 6, 1964, now abandoned.

This invention relates to perforating apparatus; and, more particularly, to shaped charge perforating apparatus for producing perforations through well casings that have burr-free entry holes.

One conventional manner of arranging shaped charge perforating apparatus is to enclose a plurality of such shaped charges within an elongated tubular and fluid-tight housing or so-called carrier. The shaped charges are mounted at longitudinally spaced intervals within the carrier with their forward ends disposed immediately adjacent to and facing toward ports in the carrier wall. These ports are typically closed by replaceable closure members. Accordingly, whenever a shaped charge is detonated, the resulting perforating jet will pierce the expendable portclosure member without damaging the body of the carrier itself. Thus, by merely replacing the expended closure members with new ones, the more expensive carrier may be reused. Expendable carriers are also widely used. Typical of these are so-called strip carriers, such as shown in Patent No. 3,048,101, or a pair of laterally spaced Wires, such as shown in Patent No. 3,282,213, which respectively support individually encapsulated shaped charges.

The typical shaped charge-whether it be supported in a hollow carrier or on an expendable carrierwill produce a perforation through a well casing that leaves an irregular annular ridge or so-called burr on the internal wall of the casing surrounding the resulting entry hole. These burrs are attributed to the radial displacement of the casing metal from the high lateral pressures developed by the perforating jet as it passes through the casing. Since the internal surface of a casing is unsupported, this displaced met-a1 can easily flow inwardly and thereby produce such irregular burrs or inward projections immediately around each entry hole.

Although these inwardly directed burrs have been a source of only minor inconvenience heretofore, their presence has not been too objectionable until recently. In one currently popular method for fracturing earth formations, a number of relatively small, elastomeric spheres or socalled ball sealers are dropped into the well bore during the course of the fracturing operation. Then, whenever the fracturing fluid develops a fracture that is in communication with one or more of the perforations, the increased flow of the fracturing fluid through these perforations will carry a corresponding number of the ball sealers into sealing engagement with the casing over the entry holes of each of these perforations. By using ball sealers with only a slightly larger diameter than the entry holes, those perforations in communication with the fractured formations will be hopefully sealed-off so that the full available fracturing pressure can be applied through the other perforations to those formations not yet broken down.

It will be appreciated, therefore, that to insure complete sealing with these ball sealers, the entry holes must be relatively smooth and regular with no uneven inward projections. The typical burr around the perforation is not, however, sufliciently regular to provide a suitable seat for ball sealers. Thus, unless these burrs are either pre- 3,34%,tl57 Patented Oct. 10, 1967 viously removed or initially prevented, ball sealers cannot be profitably utilized.

The present trend in Well completion practices is to use the smallest possible size of casing that is practical when all other factors are taken into consideration. The size of casing in a particular well will, of course, govern the size of the shaped charges and their carrier. Thus, it is usually necessary that a carrier be only slightly smaller than the internal diameter of the casing. Ordinarily this poses no particular problem.

Despite all usual precautions, however, it is not too uncommon for a shaped charge to misfire and detonate at a low-order. Aside from not producing a satisfactory perforation, when the shape-d charges are in .a retrievable enclosed carrier, the explosive force of such a low-order detonation will often partially distend or displace the adjacent port-closure member. Where such a carrier is in a well casing only slightly larger than the carrier, it is very likely that a distended or displaced port-closure member will wedge the perforating apparatus within the casing. It will be realized, of course, that should a carrier become stuck in a casing, time-consuming and expensive fishing operations must be con-ducted to remove it from the well.

Accordingly, it is an object of the present invention to provide perforating apparatus for producing entry holes in casings without leaving such objectionable burrs.

This and other objects of the present invention are provided by spacing in front of a shaped charge a rigid member having a circular aperture therein circumscribing the perforating axis of the shaped charge and of a diameter at least no greater than the expected diameter of the resulting entry hole through the casing. By pressing the rigid member against the casing, the resultant inward displacement of casing metal by the perforating jet action is restrained and no burr will be formed.

It is also a further object of the present invention to provide a new and improved port-closure member for retrievable shaped charge carriers which not only produces a smooth and uniform burr-free entry hole in the casing but also eliminates the possibility that a low-order detonation of a shaped charge might cause a port-closure member to wedge the carrier in the casing.

This further object of the present invention is accomplished by providing for use with retrievable carriers a port-closure member having a forward rigid portion with a transverse curvature adapted for complementary contact with the inner surface of a casing to be perforated. A circular apertureis arranged in the forward portion to circumscribe the perforating axis of a shaped charge to be disposed opposite that port. In addition to making the diameter of this aperture no greater than the expected diameter of the resulting entry hole through the casing, it may also be sized in relation to the anticipated diameter of the perforating jet so that an abnormal enlarged irregularity in the trailing portion of the jet will contact the wall defining the aperture and be dissipated and reduced thereby. A web member of a predetermined thickness is spaced apart and to the rear of the circular aperture so as to close the port-closure member until detonation of its associated shaped charge and to define a chamber between the web and aperture. Laterally extending passage means between this chamber and the exterior of the port-closure member allow gases to be vented from the interior of the carrier upon failure of the web from excessive gas pressure created by a loworder detonation of the associated shaped charge.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation together with further objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a longitudinal view, partially in cross-section, of typical shaped charge perforating apparatus employing the port-closure members of the present invention and shown operatively disposed in a well bore;

FIG. 2 is an elevational view of a port-closure member constructed in accordance with the present invention;

FIG. 3 is a cross-sectional view taken along the lines of 33 of FIG. 2;

FIG. 4 depicts one form of a malformed perforating j FIG. 5 is an enlarged cross-sectional view showing a port-closure member of the present invention after being pierced by the normal action of its associated shaped charge;

FIG. 6 is a view similar to FIG. 5, but shows a portclosure member of the present invention after its as-' sociated shaped charge has detonated at low-order;

FIG. 7 is an elevational view, partially in cross-section, of a typical enclosed, hollow carrier for shaped charges with another embodiment of the present invention;

FIG. 8A is a cross-sectional plan view of the perforator shown in FIG. 7 taken along the transverse lines 88 before the perforator is actuated;

FIG. 8B is a cross-sectional plan view similar to FIG. 8A, but after the perforator has been actuated; and

FIG. 9 is an elevational view of a typical retrievable expendable carrier supporting encapsulated shaped charges and including a further embodiment of the present invention.

Turning now to FIG. 1, a retrievable, reusable steel carrier 10 suspended in the ususal manner from an electrical cable 11 is shown disposed within a casing 12 secured within a well bore 13 by cement 14 in the annulus therearound. A plurality of conventional shaped charges 15 are mounted at longitudinally spaced intervals within the fluid-tight interior of the carrier 10 with their forward ends facing in the same direction and disposed opposite to and in axial alignment with longitudinally spaced radial ports 16 in the wall of the carrier along a comm-on longitudinal axis. Port-closure members 17 arranged in accordance with the present invention are fluidly sealed and secured within each of the ports 16. Thus, whenever a shaped charge 15 is detonated, the perforating jet will pass through the center of its respective portclosure member 17 The carrier 10 has positioning means, such as a plurality of magnets 18 mounted on the common longitudinal axis of the port-closure members 17 for laterally shifting the carrier to place the port-closure members close to the wall of the casing 12. It will be realized, of course, that other devices would be equally suitable for displacing the carrier 10 against the casing 12 for the present invention to be effective.

Turning now to FIGS. 2 and 3, a port-closure member 17 of a suitable rigid material, such as steel, and constructed in accordance with the present invention is shown in greater detail. The port-closure member 17 has a generally cylindrical body portion 18 with an enlarged forward portion or head 19. The body portion 18 is externally threaded, as at 20, to threadedly secure the closure member 17 within a port 16 in a carrier 10 such as that shown in FIG. 1. The exterior surface 21 of the forward head portion 19 of the port-closure member 17 is formed with a spherical curvature that will be substantially complementary in a transverse plane to a portion of the internal curvature of a well casing. A blind axial bore 22 extends substantially through the body portion 18 and is terminated with an internal frusto-conical end surface portion 23. First and second coaxial bores 24, of different lengths and diameters are formed in the head portion 19 and directed along the central axis toward the rear of the closure member 17. The bore 24 of the greater diameter is terminated first to provide a forwardly directed annular shoulder 26 proximate to the curved surface 21 of the head portion 19. The longer second bore 25 is of a lesser diameter and is terminated, as best seen in FIG. 3, to leave only a thin rupturable web 27 of a predetermined thickness separating the second bore 25 from the internal bore 22 within the body portion 18.

A plurality of shallow, transverse recesses or slots 28, 29 are formed in the exterior surface 21 of the head portion 19 of the port-closure member 17 and extended radially outwardly from the central axis of the closure member. An annular rigid member 30 having a central opening or aperture 31 of a predetermined diameter and an external diameter of an appropriate size is received within the first coaxial bore 24. The annular member 30 is secured in place with its rearward face resting on the forwardly directed annular shoulder 26 formed at the intersection of coaxial bores 24 and 25, and its forward face 32 substantially flush with the spherically curved surface 21 of the head portion 19. Although this annular member 30 is usually of steel or similar metals, it is equally effective when made of other rigid materials such as ceramics or frangible cast irons.

Referring now to FIG. 4, a fully developed perforating jet 33 extending along the central axis 34 of a shaped charge (not shown) is schematically illustrated. A perforating jet 33 typically includes forward and rearward portions 35 and 36 which usually have a uniform configuration about the central axis 34. The forward portion 35 of the jet 33 is first generated and ordinarily is welldefined and has a relatively small diameter d. The trailing or rearward portion 36 of the jet 33 has a determinable length I. This length I may be easily determined by conventional procedures such as observing radiographs of a jet and examining conventional test targets.

Experience has shown, however, that when a shaped charge is detonated, there will often be some small defect tending to enlarge and often distort the trailing portion 36 of a jet. As shown in FIG. 4, such defects may take the form of an eccentric enlargement 37 of the trailing portion 36. When this occurs during actual service, such an enlargement 37 will produce an irregular or keyshaped entry hole in the casing. Irregular entry holes are recognized as being particularly objectionable where, as previously mentioned, ball sealers are subsequently used to seal-off the perforations during limited-entry fracturing operations.

It has been found, however, that such irregularly shaped entry holes will be substantially eliminated by making the diameter of the central opening 31 through the annular member 30 only slightly greater than the anticipated dlameter d (FIG. 4) of the perforating jet 33 for that partrcular style of shaped charge. Thus, as best seen in FIG. 5, when a shaped charge 15 is detonated, it will be seen that the perforating jet must pass through the central openmg 31 of the annular member 30 before it reaches the casing 12. The well-defined forward portion of the perforating jet will pass through the central opening 31 without coming into appreciable contact with the annular member 30. Should the trailing portion of the perforating et be enlarged, however, as that portion passes through the central opening 31, it will come into contact with and consume at least a portion of the annular member 30. Thus, in this manner, the potential energy of irregularities in the trailing portion of the perforating jet will be partially dissipated and reduced to a level where the uniform entry hole 38 through the casing 12 produced by the forward portion of the jet will not be irregularly enlarged by the traihng jet portion. It has been found that the characterrstics of the perforation 39 in the formation 40 are substantially unaffected.

It has also been found that irrespective of whether a et has an irregular or enlarged trailing portion, where the annular member 30 is in close proximity to or is engaged against the inner surface of the casing 12 as shown in FIG. 5, there will be no annular inwardly directed protrusron or burr formed around the entry hole 38.

It is believed that the annular rigid member 30 prevents the metal displaced from the casing 12 from flowing radially inwardly and around the entry hole 38 and forming the aforementioned objectionable burrs.

Turning now to the other cooperative features of the port-closure members 17. It has been found that by sizing the thickness of the web 27 (FIG. 3) to be only substantially what is required to withstand anticipated well bore pressures, the web will be sheared and displaced outwardly as shown in FIG. 6 should a shaped charge 15 adjacent thereto detonate at only a low-order. Thus, in such an instance, whatever explosive pressure that is developed in the carrier by a low-order detonation will be quickly dissipated by failure of the web 27 rather than, as heretofore, by distending the forward portion of a conventional port-closure member or even forcing that member partially out of its threads. Inasmuch as the perforating carrier 10 is intended to be held in contact against the casing 12, the transverse recesses 28, 29 will always provide open channels for venting the explosive gases as they escape through the failed web portion 27 as indicated by the arrows 42.

Accordingly, it will be appreciated that the port-closure member 17 of the present invention has provided new and improved cooperative means for insuring that a regularly formed and uniform burr-free entry hole will be produced in a well casing. Moreover, in the event that a shaped charge in the carrier 10 misfires and is detonated at only low-order, the new and improved port-closure members 17 of the present invention provide means for safely relieving the still substantial explosive forces in such a manner that the carrier will not be wedged within a casing.

Turning now to FIG. 7, perforating apparatus 50 including a typical reusable hollow carrier 51 similar to that at 10 in FIG. 1 is shown suspended in the wellbore 13 by the electrical cable 11. Although the depicted carrier 51 is of the type that may be reused, it will be understood, however, that the present invention can be used with equal success with a retrievable but expendable hollow carrier, such as that shown in Patent No. 3,048,102.

The perforating apparatus 50 further includes a plurality of shaped charges 52 that are supported in some convenient manner at longitudinally spaced intervals in the fluid-tight interior of the carrier 51, with the central axis of each shaped charge being transverse to the longitudinal axis of the carrier. Although the shaped charges 52 may be faced in only two or three transverse directions, it is preferred to alternately orient the shaped charges at spaced intervals, such as at 90 intervals as shown in FIG. 7, so as to produce a respective number of perforations at corresponding 90 intervals around the internal circumference of the casing 12. To detonate the shaped charges 52, a detonating cord 53 is secured in the usual fashion along the rear of each shaped charge and terminated at a typical electrically responsive detonator (not shown) in the lower portion of the carrier 51. Conventional replaceable port plugs 54 are fluidly sealed in complementary lateral access ports formed in the wall of the carrier 51 and arranged immediately in front of each shaped charge 52 and in coincidental alignment with the perforating axis of their associated shaped charge.

In accordance with the present invention, four longitudinally disposed rigid members 55 are equally spaced at 90 intervals around the periphery of the carrier 51 and held away therefrom by resilient support means, such as springs or reversely bowed arms 56 and 57 near each end of the rigid members and respectively secured to the carrier. So that the perforating apparatus 50 may easily accommodate various diameters of casing 12 with a reasonable degree of freedom, the arms 56 and 57 are made of suflicient flexibility that the members 19 may retract slightly should they strike an obstruction or should it be necessary for them to retract upon entering a section of the casing with a smaller internal diameter. The outer or forward faces of the longitudinal members 55 are appropriately configured in a transverse plane to have a curvature at least substantially complementary to the internal wall of the casing 12. Thus, when the perforating apparatus is in the well bore 13, at least a substantial portion of the forward faces of the elongated members are firmly urged against a sector of the casing 12 by the biasing action of the bowed arms 56 and 57. It will be appreciated, of course, that where at least three of the elongated members 55 are employed, the bowed arms 56, and 57 of each member will cooperate as positioning means to urge the other members against the casing 12. Where, however, perforating apparatus such as that shown in FIG. 1, is used with the shaped charges facing in only one direction, positioning means such as shown there at 1% or at 168 and 109 in FIG. 9 hereof would be used.

The elongated rigid members 55 are so oriented with respect to the transverse axes of the carrier 51 that the members are respectively positioned directly in front of those port plugs 54 that have their central axes in a common longitudinal plane along the carrier. In addition, the present invention includes a plurality of circular holes, as at 58 for example, formed at longitudinally spaced intervals in each of the elongated members 55 to respectively locate one of the holes in coincidental alignment with the perforating axis 5 of an associated one of the shaped charges 52. Thus, whenever the shaped charges 52 are detonated, the resulting perforating jets must each pass through a corresponding one of the holes 58 in the elongated members 55 before reaching the casing 12.

Turning now to FIG. 8A, a transverse cross-sectional view is shown of the carrier 51 and of one of the shaped charges 52 therein. The shaped charge 52, its respective port plug 54 and the hole 58 in the elongated member 55 associated therewith are all coincidentally aligned along the anticipated perforating axis 59 of the shaped charge. Moreover, as further seen in this figure, the curved forward face of the elongated member 55 is firmly engaged against the adjacent internal surface of the casing 12 in readiness for detonation of the shaped charge 52.

Accordingly, as best seen in FIG. 8B, high order detonation of the shaped charge 52 will produce a perforating jet 60 that, as it progressively proceeds along its axis 59, pierces the port plug 54, passes through the hole 58, and develops a perforation 61 through the casing 12 and cement 14 that terminates in the formation 62 therebeyond. It will be further noted that the expected diameter of the resulting entry hole 63 through the casing 12 is somewhat larger than the hole 58 in the elongated member 55. Moreover, the diameter of the hole 58 in the elongated member 55 is also slightly larger than the anticipated diameter of the perforating jet 60. Thus, the passage of a normal perforating jet will have no particularly deleterious effect upon either the elongated member 55 or the internal surfaces of the holes 58. It will be realized, of course, that the holes 58 can also be sized in the same manner as previously discussed with respect to the hole 31 through the annular member 30.

Of more particular significance, it will be seen that no objectionable burr is formed on the internal wall of the casing 12 around the entry hole 63. Instead, it has been found that the restraint afforded by urging of the elongated member 55 against the adjacent surface of the casing 12 prevents the inward displacement of metal into the casing and instead diverts this metal either radially away from the entry hole 63 or outwardly toward the outside of the casing as at 64. This radial displacement of metal, of course, accounts at least in part for the diameter of the entry hole 63 being appreciably larger than the diameter of the perforating jet 60. Accordingly, by using the present invention, the internal wall of the casing 12 is left substantially smooth around the entry holes, such as at 63, to insure fluid-tight seating of the typical sealing balls employed in subsequent fracturing operations.

Turning now to FIG. 9, another embodiment of perforating apparatus 100 also arranged in accordance with the present invention is shown with a typical retrievable carrier 101 supporting a plurality of longitudinally spaced encapsulated shaped charges 102. By way of example, the carrier 101 depicted in FIG. 9 is a so-called expendable strip carrier such as shown in Patent No. 3,048,101. It will be recognized, of course, that other expendable carriers employing laterally spaced wires such as shown in Patent No. 3,282,213, could be used with equal success.

A fluid-tight detonating cord 103 is appropriately secured to the rear of each of the shaped charges 102 and arranged for selective detonation by an electrically responsive detonator 104 connected to the suspension cable 11. A longitudinally disposed, elongated member 105 similar to those shown at 55 in FIG. 7 is laterally spaced in front of the shaped charges 102 and yieldably secured to the carrier 101 by resilient means such as reversely bowed arms 106 and 107 at each end of the elongated member. Positioning means, such as extendible springbiased arms 108 and 109 near each end of the carrier 101 and oriented 180 away from the member 105, urge the curved forward face of the elongated member into complementary engagement with the casing 12 in the same manner as already described with respect to FIGS. 1-7. It will be recognized as well that if it is desired to orient the shaped charges 102 in opposite directions, another outwardly urged elongated member, such as that at 105, could be used instead of the spring-biased arms 108 and 109.

Accordingly, it will be appreciated that the present invention employs a substantially rigid member having a forward face that is complementarily curved in at least a transverse direction to conform to the casing and which is held thereagainst by suitable positioning means. By forming a circular hole in the rigid member that circumscribes the perforating axis of a shaped charge and which has a diameter at least no larger than the expected diameter of the resulting entry hole in the casing, no burr is left. Moreover, by making the diameter of the circular hole slightly greater than the anticipated perforating jet, it can quite easily pass through this hole with little or no damage to the rigid member. Thus, the elongated members, such as at 55 and 105, can be reused for purposes of economy.

It will be realized, therefore, that by restraining any tendency of the casing metal to be displaced toward the interior of the casing, there will be no objectionable projection or burr left around the resulting entry hole. In this manner, satisfactory performance of ball sealers in subsequent fracturing operations will be insured. It will also be appreciated that the elongated members of the present invention will permit the shaped charges to be directed in more than one transverse direction. Thus, the resulting perforations can be scattered around the full circumference of the well bore rather than being limited to only a single transverse direction.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Apparatus for providing a uniform burr-free open ing in a well casing comprising: perforating means including a shaped charge for developing, upon its detonation, a perforating jet directed along a predetermined axis to perforate an adjacent surface of a well casing and produce an entry hole therein of an expected diameter; means for confining the adjacent casing surface including a rigid member spaced forwardly from said shaped charge and having a circular aperture therethrough of a diameter no greater than said expected entry hole diameter and circumscribing said perforating axis, the outer face of said rigid member having a transverse cuivature that is substantially complementary to the adjacent casing surface; and positioning means for urging said outer face of said rigid member into complementary contact with the adjacent casing surface.

2. The apparatus of claim 1 wherein the diameter of said circular aperture is no smaller than about that of said perforating jet.

3. The apparatus of claim 1 further including a fluidtight capsule around said shaped charge; means for supporting said capsule; and means on said support means for supporting said rigid member.

4. The apparatus of claim 3 wherein the diameter of said circular aperture is no smaller than about that of said perforating jet.

5. The apparatus of claim 1 further including a hollow carrier enclosing said shaped charge; and means on said carrier for supporting said rigid member.

6. The apparatus of claim 5 wherein the diameter of said circular aperture is no smaller than about that of said perforating jet.

7. The apparatus of claim 5 further including an inner wall spaced between said shaped charge and said rigid member to define a space therebetween, said inner wall having a thin-walled section intersecting said perforating axis; and means for venting explosive gases from said carrier including passage means communicating said space to the exterior of said carrier for bypassing such gases relative to said circular aperture.

8. Apparatus for providing a uniform burr-free opening in a well casing comprising: a hollow carrier having a central axis; perforating means including a plurality of shaped charges mounted at longitudinally-spaced intervals within said carrier for developing, upon their detonation, a corresponding number of perforating jets directed along predetermined perforating axes transverse to said central carrier axis to perforate an adjacent surface of a well casing and produce a corresponding number of longitudinally-spaced entry holes therein of expected diameters; means for confining the adjacent casing surface including an elongated rigid member spaced outwardly from and generally parallel to said carrier and having a plurality of circular apertures therethrough at said longitudinallyspaced intervals through which said perforating jets will respectively pass, each of said circular apertures having a diameter no greater than said expected entry hole diameters and each respectively circumscribing one of said perforating axes, said elongated member having an outer face with a transverse curvature that is substantially complementary to the adjacent casing surface; means for supporting said elongated member on said carrier; and positioning means for urging said outer face of said elongated member into complementary contact with the adjacent casing surface.

9. The apparatus of claim 8 wherein said shaped charges are facing in the same direction.

10. The apparatus of claim 8 wherein the diameters of said circular apertures are no smaller than about those of said perforating jets.

11. The apparatus of claim 8 further including a second plurality of shaped charges mounted at longitudinally-spaced intervals in said carrier for developing, upon their detonation, a corresponding number of second perforating jets directed along predetermined perforating axes transverse to said central carrier axis but in a different direction than that of said first perforating axes to perforate a second adjacent surface of the casing and produce a corresponding number of second longitudinally-spaced entry holes therein of expected diameters; and second means for confining the second adjacent casing surface including a second elongated rigid member spaced outwardly from and generally parallel to said carrier and having a second plurality of circular apertures therethrough at said second longitudinally-spaced intervals through which said second perforating jets will respectively pass, each of said second circular apertures having a diameter no greater than said expected entry hole diameters and each respectively circumscribing one of said second perforating axes, said second elongated member having an outer face with a transverse curvature that is substantially complementary to the second adjacent casing surface.

12. The apparatus of claim 11 wherein said first and second pluralities of shaped charges are facing in opposite directions; and wherein said supporting means include spring members and said positioning means comprise said first and second elongated members being on opposite sides of said carrier for respectively urging the other of said elongated members into complementary contact with their respective adjacent casing surface.

13. The apparatus of claim 11 wherein the diameter of said first and second circular apertures are no smaller than about those of said perforating jets respectively passing therethrough.

14. Apparatus for providing a uniform burr-free opening in a well casing comprising: an elongated carrier having a central axis; perforating means including a plurality of encapsulated shaped charges mounted at longitudinally-spaced intervals on said carrier for developing, upon their detonation, a corresponding number of perforating jets directed along predetermined perforating axes transverse to said central carrier axis to perforate an adjacent surface of a well casing and produce a corresponding number of longitudinally-spaced entry holes therein of expected diameters; means for confining the adjacent casing surface including an elongated rigid member spaced outwardly from said shaped charges and generally parallel to said carrier and having a plurality of circular apertures therethrough at said longitudinallyspaced intervals through which said perforating jets will respectively pass, each of said circular apertures having a diameter no greater than said expected entry hole diameters and each respectively circumscribing one of said perforating axes, said elongated member having an outer face with a transverse curvature that is substantially complementary to the adjacent casing surface; means for supporting said elongated member; and positioning means for urging said outer face of said elongated member into complementary contact with the adjacent casing surface.

15. The apparatus of claim 14 wherein said shaped charges are facing in the same direction.

16. The apparatus of claim 14 wherein the diameters of said circular apertures are no smaller than about those of said perforating jets.

17. Apparatus for providing a uniform burr-free opening of an expected diameter in a well casing comprising:

a hollow carrier having a port therein; a port-closure member closing said port, said port-closure member having a rigid outer portion and a thin-walled inner portion spaced inwardly therefrom and defining a space therebetween, said outer portion having a circular aperture therein of a diameter no greater than said expected diameter and an outer face with a transverse curvature adapted for complementary contact with a casing; and perforating means including a shaped charge disposed in said carrier for developing, upon detonation, a perforating jet directed through said port-closure member along a predetermined axis intersecting said thin-walled inner portion and extending through said circular aperture.

18. The apparatus of claim 17 further including means for venting explosive gases from said carrier comprising passage means communicating said space to the exterior of said port-closure member for bypassing such gases relative to said circular aperture.

19. The apparatus of claim 18 wherein said portclosure member has a tubular body portion secured in said port and an enlarged head portion, said rigid outer portion being in said enlarged head portion and said thinwalled inner portion being in said tubular body portion.

20. The apparatus of claim 19 wherein said enlarged head portion has a forwardly-directed recess in said outer face thereof and said rigid outer portion is an annular rigid member secured in said recess.

21. As a subcombination for use with shaped explosive charge perforating means: a hollow carrier having a port therein; a port-closure member having a tubular body portion secured in said port and an enlarged head portion having a spherical forward face with a forwardly directed recess therein; a thin-walled section closing the bore of said tubular body portion and defining a space in said bore inwardly from said recess; perforating jet regulating means including a rigid member having a circular opening therein mounted in said recess with its forward face flush with said spherical forward face; and means for relieving pressure within said carrier including passage means providing communication from said space to the exterior of said carrier.

References Cited UNITED STATES PATENTS 2,587,244 2/1952 Sweetman 4.6 2,616,370 11/1952 Foster 1754.53 2,952,319 9/1960 Popham 166-35 3,268,016 8/1966 Bell 1754.51

CHARLES E. OCONNELL, Primary Examiner. DAVID H. BROWN, Examiner, 

1. APPARATUS FOR PROVIDING A UNIFORM BURR-FREE OPENING IN A WELL CASING COMPRISING: PERFORATING MEANS INCLUDING A SHAPED CHARGE FOR DEVELOPING, UPON ITS DETONATION, A PERFORATING JET DIRECTED ALONG A PREDETERMINED AXIS TO PERFORATE AN ADJACENT SURFACE OF A WELL CASING AND PRODUCE AN ENTRY HOLE THEREIN OF AN EXPECTED DIAMETER; MEANS FOR CONFINING THE ADJACENT CASING SURFACE INCLUDING A RIGID MEMBER SPACED FORWARDLY FROM SAID SHAPED CHARGE AND HAVING A CIRCULAR APERTURE THERETHROUGH OF A DIAMETER NO GREATER THAN SAID EXPECTED ENTRY HOLE DIAMETER AND CIRCUMSCRIBING SAID PERFORATING AXIS, THE OUTER FACE OF SAID RIGID MEMBER HAVING A TRANSVERSE CURVATURE THAT IS SUBSTANTIALLY COMPLEMENTARY TO THE ADJACENT CASING SURFACE; AND POSITIONING MEANS FOR URGING SAID OUTER FACE OF SAID RIGID MEMBER INTO COMPLEMENTARY CONTACT WITH THE ADJACENT CASING SURFACE. 